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High7.5Red Hat Linux

High [CVE-2026-4721] Memory safety bugs fixed in Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149

This high-severity Red Hat Linux advisory covers CVE-2026-4721 affecting Red Hat Enterprise Linux 10.0 Extended Update Support, Red Hat Enterprise Linux 7 Extended Lifecycle Support, Red Hat Enterprise Linux 8.2 Advanced Update Support.

CVE-2026-4721 Published Mar 24, 2026
CVE-2026-4721
Affected products & platforms
Red Hat LinuxUnclassified
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Summary

Memory safety bugs fixed in Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149. Red Hat rates this important (CVSS 7.5).

Weakness: CWE-825. Affected package(s): firefox, thunderbird.

Resolved in Red Hat advisory RHSA-2026:6917 — update the affected packages (`sudo dnf update`).

Affected products named by the advisory: Red Hat Enterprise Linux 10.0 Extended Update Support; Red Hat Enterprise Linux 7 Extended Lifecycle Support; Red Hat Enterprise Linux 8.2 Advanced Update Support; Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support; and 10 more.

Affected versions
  • firefox-0:140.9.0-1.el8_10
  • thunderbird-0:140.9.0-1.el8_10
  • firefox-0:140.9.0-1.el8_4
  • firefox-0:140.9.0-1.el9_2
  • firefox-0:140.9.0-1.el8_2
  • firefox-0:140.9.0-1.el9_0
  • firefox-0:140.9.0-1.el7_9
  • firefox-0:140.9.0-1.el8_8
  • firefox-0:140.9.0-1.el9_7
  • firefox-0:140.9.0-1.el9_6
  • firefox-0:140.9.0-1.el8_6
  • firefox-0:140.9.0-1.el9_4

Official advisory · high-confidence parse· fetched 2 months ago·verify at source

Fixed versions
  • RHSA-2026:6917

Official advisory · high-confidence parse· fetched 2 months ago·verify at source

Mitigation checklist

Recommended fix / mitigation
  • Update the affected package(s) to the fixed version shipped in RHSA-2026:6917 (`sudo dnf update` / `yum update`).

Official advisory · high-confidence parse· fetched 2 months ago·verify at source

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